1. Technical Field
Embodiments described herein relate to relates to an illumination optical system, a light source device having the illumination optical system, and a projector having the light source device.
2. Related Art
Nowadays, data projectors are used frequently as image projecting devices for projecting, onto a screen, a displayed image of a personal computer, a video image, an image that is produced based on image data stored in a memory card or the like, and other images. Such projectors display a color image on a screen by condensing light emitted from a light source on a micro-mirror display device called DMD (digital micro-mirror device) or a liquid crystal plate.
With the spread of personal computers and video equipment such as DVD players/recorders, uses of projectors are expanding which include business presentation and home use. Whereas previously projectors mainly employed a high-luminance discharge lamp as a light source, in recent years many projectors that employ a semiconductor light-emitting device such as a laser diode as a light source have been developed or proposed. In this connection, illumination optical systems are known in which a fluorescence is excited by laser light and resulting fluorescent light emitted from the fluorescence is used as light-source light. JP-A-2003-295319 discloses a projector in which incoherent light that is emitted from a fluorescence when it is illuminated with condensed laser light is converted into parallel light by a reflector.
The present applicant proposed, in a prior patent application, a light source unit which is equipped with a blue laser diode, a fluorescence wheel in which a fluorescent light emitting region in which a green fluorescence layer is formed on a reflection surface and a diffuse transmission region in which an opening is provided with a diffuse transmission plate are arranged in the circumferential direction, and a red light-emitting diode. In this proposal, light emitted from the red light-emitting diode is used as light-source light in a red wavelength band, light emitted from the green fluorescence layer when it is illuminated with light emitted from the blue laser diode (excitation light) is used as light-source light in a green wavelength band, and light that originates from the blue laser diode and is diffuse-transmitted by the diffuse transmission plate is used as light-source light in a blue wavelength band.
In the projector disclosed in Patent document 1, the efficiency of utilization of emission light can be made high in the case where light emitted from the fluorescence when it is illuminated with excitation light emitted from a laser diode (excitation light source) is converted into parallel light by the reflector. However, this projector is associated with a problem that a projected image is prone to have unevenness in screen illuminance.
In the projector in which blue laser light is diffused by the diffusing plate is projected onto a screen, illuminance unevenness can be prevented by increasing the diffusion angle of the diffusing plate. However, the absolute value of illuminance may be reduced by loss that is caused by an increased diffusion angle. Therefore, an illumination optical system capable of capturing diffused light as efficiently as possible is necessary.